1. Field of the Invention
The present invention relates to a two dimensional image recording and reproducing scheme to be used for the optical information recording.
2. Description of the Related Art
The known schemes for recording and reproducing information as a two dimensional image includes a QR (Quick Response) code developed by Denso corp. in 1994 and a data matrix developed by United Parcel Service Inc. in late 1980s, which are known as the two dimensional codes. The two dimensional code is a scheme for recording information in two directions, horizontal and vertical directions, which is capable of recording information in an amount that is several ten to several hundred times more than a one dimensional code such as the bar code.
The two dimensional code has extraction symbols to be used in extracting information and timing marks for indicating a position and a size of each cell. The reproduction of the information is realized by reading the image by using a scanning device such as CCD (Charge Coupled Device) camera, converting it into a binary image, detecting the extraction symbols and the timing marks, and judging which pixel on the image is black and which pixel on the image is white.
The QR code uses a method for detecting the extraction symbol that is different from the data matrix. The QR code has rectangular extraction symbols provided at three corners, and this extraction symbol is designed such that a specific pulse signal can be detected from it. This method enables the high speed extraction position detection.
On the other hand, the data matrix has an extraction symbol in a form of an L-shaped guide line, and this guide line cannot be detected by the pulse detection unlike the case of the QR code so that some software processing is required.
However, the prior art as described above has been associated with the following problems.
In the general two dimensional code of the prior art described above, a size of one pixel that expresses black or white is a far larger than a size of a pixel of the scanning device. In other words, in the case of detecting one pixel, the detection is made by a plurality of pixels of the scanning device so that it becomes easier to judge whether it is white or black and a rate of the detection error due to noises or the like is low. However, it becomes difficult to store a large amount of information within a small region, so that it is difficult to increase the storing density.
Also, in the two dimensional image with large noises such as a holographic image, a rate of a grey portion that is neither black nor white becomes large due to the poor contrast, so that it becomes very difficult to judge whether it is white or black, and it is difficult to detect the specific pulse signal such as that of the QR code.
Also, in the case of carrying out the data reading and the position detection in units of one pixel of the scanning device, when a pixel displacement occurs between pixels of the recording image and pixels of the scanning device, it is difficult to make the detailed detection and it is difficult to detect the position accurately because the position detection can only be made in units of pixels.